CVE-2026-52845Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`
Updated under an hour ago ()
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It affects caddyserver caddy and 1 other product. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
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Caddy is an extensible server platform that uses TLS by default. Prior to 2.11.4, forward_auth copy_headers deletes the exact client-supplied identity header before copying the trusted value from the auth gateway. But when the request later goes through php_fastcgi, Caddy normalizes HTTP headers into CGI variables by replacing - with _. This lets a client send an underscore alias that survives the forward_auth delete step but becomes the same PHP/FastCGI variable. Result: a remote client can inject or sometimes override identity/group headers trusted by PHP/FastCGI applications behind Caddy. This vulnerability is fixed in 2.11.4.
- CVSS
- 8.1 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
- Weakness (CWE)
- CWE-287, CWE-290, CWE-444
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- GitHub_M
- NVD analysis
- Modified
- Record last updated
- Jul 14, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
caddyserver caddy caddyserver:caddy (from the name) | before 2.11.4 | CNA record |
Red Hat Red Hat Hardened Images redhat:hummingbird | 1 | CISA ADP |
caddyserver caddy caddyserver:caddy | before 2.11.4 | NVD |
References
- https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45gx-refsource-confirm, exploit, third-party-advisory
- https://access.redhat.com/security/cve/CVE-2026-52845
- https://bugzilla.redhat.com/show_bug.cgi?id=2491907
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52845.json
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.